The operational requirements of combustion engines are becoming more and more demanding. Exhaust gas emission requirements of internal combustion piston engines become more and more stringent. In order to cope with such requirements there are various techniques available by means of which the gaseous emissions may be controlled when the engine is running. The timing of the inlet valves plays significant role in the engine performance. Particularly, it has an effect of temperature and pressure prevailing in the cylinder and thus a formation of gaseous pollutants such as NOx emissions.
U.S. Pat. No. 2,670,595 discloses a so-called Miller cycle wherein the inlet valve is closed before the piston reaches the bottom dead center of the intake stroke. After closing of the inlet valve, the charge, or air, in the cylinder expands resulting in decreasing the pressure and the temperature or the charge.
U.S. Pat. No. 7,395,668 B2 discloses a turbo-charged diesel-type piston engine and method for controlling such an engine which the thermal efficiency of the internal combustion engine can be increased while the requirements relating to nitrogen oxide and soot particle emissions continue to be maintained.
WO 2014/126737 A1 discloses a control system of a gaseous fuelled engine with a cam phaser for improving the engine start. The control system may have variable inlet valve timing device configured to adjust a cyclical closing timing of the inlet valve. A controller may be configured to selectively initiate a first Miller cycle timing and a second Miller cycle timing.
WO 2011/135162 A1 discloses a control arrangement for a gas exchange valve in a piston engine adapted between the camshaft of the engine and the valve mechanism. The control arrangement comprises a chamber that is in connection with a hydraulic medium and in which a piston is movably arranged to be in mechanical force transmission connection with the camshaft and the valve mechanism at least for opening the valve.
In a case of a malfunction in operation of the inlet valve system, particularly controlling the closing timing of the inlet valve, pressure in the cylinder may increase significantly which has undesirable consequences. In some cases that may even damage the inlet valve system and parts in connection with the cylinder.
An object of the invention is to provide a method of controlling an operation of an inlet valve system, and an inlet valve control system in which the performance is considerably improved compared to the prior art solutions.